Repair and waterproofing of a leaking flat roof

Repair and waterproofing of a leaking flat roof

Terraces and flat roofs have a protective function in a building.

In addition, they are areas permanently subjected to very adverse weather conditions.

Therein lies the special importance of properly waterproofing them.

Preliminary analysis

It is important to analyze all the constituent components of a flat roof, in order to partially maintain it and maintain the continuity of the waterproofing.

The constituent materials of a terrace are not waterproof in themselves. It is the overlapping and correct positioning that will afford us good protection against water.

All possible fissures that can allow the entrance of water must be examined and proceed to remove all broken or damaged ceramic elements.

With the passage of time, the impermeability provided by the installation of asphalt sheets is affected and will suffer cracks that will be a source of future problems.

To waterproof a flat roof, we must use a material that prevents the passage of water, resists environmental aggressions and protects all the roof materials.

Technical considerations

As a previous step, we must adequately prepare the substrate.

To this end:

  • Firstly, we must remove all the degraded parts and clean the substrate, filling the previously emptied joints with a repairs mortars of the GECOL Reparatec range.
  • Junctures between floors and walls must be properly sealed to avoid the entrance of water.
  • It is advisable bridge expansion joints using synthetic fiberglass cloth.
  • Expansion joint seals must be cleaned and resealed if deteriorated using the elastic mastic G#color Elastic-MS.
  • After correctly cleaning the flat roof floor, we will proceed to waterproof the substrate using GECOL Imper-E.
  • To guarantee the minimum thickness of 2 mm throughout our waterproofing, the use of a mesh resistant to alkalis GECOL Malla-70 is recommended, paying the utmost attention in the realization of the wall-wall and wall-pavement encounters.
  • If this system is going to bear traffic, it requires cladding with ceramic material, for which purpose we must use a flexible and high performance like G100 Flexible premium.

Recommended products

Concrete rapairers



Structural-fast setting


Thin layer 3 mm Elastic

Fast setting

Flexible mastic

Elastomeric mastic


Warnings: The data provided by this Constructive Solution were prepared based on standard onsite installation processes. However, we recommend that you consult our Technical Department in the event of any specific circumstance